The present invention is directed generally to circuits and elements for managing electrical signals and, in particular, to circuits and elements for applying a variable resistance to electrical signals passing therethrough.
In managing and operating electrical signals (which may include radio frequency ("RF") signals), it is frequently desirable to vary the resistance applied to such signals based upon the frequency of the signals. To provide for such varying resistance, the prior art is replete with circuits for varying the resistance of a portion of a circuit in response to a detected frequency of a signal being carried. For example, it is known in the prior art to utilize a subcircuit in which plural resistors are interconnected by switches so that electrical signals can be passed from one end of the subcircuit to the other end while experiencing different amounts of resistance, depending upon the switch settings which, in turn, change the amount of resistance placed in the path between the ends of the subcircuit. The resistors can be switched into and out of the subcircuit in a parallel or serial fashion to provide a wide variety of resistance choices for the differing signals passing therethrough. As is known in the art, the operation of the switches may be made dependent on the frequency of the passing signal as detected by a conventional frequency detector. The use of such frequency varying resistance devices is relatively complex, given the number of switches which may be involved and the complexity of a reliable frequency determination circuit. Such devices, therefor, add both to the complexity and cost of a circuit wherein they are used. In addition, such devices may diminish the overall reliability of the circuit in which they are used.
There are also many different devices and circuits in the prior art in which the resistance of the device/circuit varies as a function of the frequency of signals being passed therethrough. Many of such devices use inductive and/or capacitive elements which permit the circuit to respond variably to frequency but which often place a lag in the signal being passed therethrough and may generate harmonic or similar undesired signals.
In one prior art circuit, a filter in a bridge configuration utilized a Whetstone bridge in which the resistive elements were composed of a metal conductor coated with a second metal. As the frequency of the signals being passed through the resistive elements was increased, the "skin effect" caused the current to change the path of its flow from the central conductor to the second metal coating on the "skin" of the element. Thus, as the frequency of the current increased, the current experienced a variation in the resistance experienced as the current flowed first through one type of metal (the metal of the conductor) and then to a second type of metal (the metal of the coating). See, for example, the Schlachter U.S. Pat. No. 3,704,434, issued Nov. 28, 1972.
Accordingly, it is an object of the present invention to provide a novel element and circuit in which the resistance of the element or circuit varies with the frequency of the signal being passed therethrough.
It is another object of the present invention to provide a novel element and circuit having a frequency dependent resistance which does not require an active frequency determination.
It is yet another object of the present invention to provide a novel element and circuit having a frequency dependent resistance which does not require the switching among different elements.
It is still another object of the present invention to provide a novel element and circuit having a frequency dependant resistance which does not require different materials be used in the current carrying portions of the element.
It is a further object of the present invention to provide a novel element and circuit having a frequency varying resistance in which the shape of the element determines its varying resistance characteristics.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.